1. Field of the Invention
The present invention generally relates to downhole tools for use in a wellbore. More particularly, the invention relates to a downhole tool for sealing a wellbore, such as a hydrocarbon wellbore. More particularly still, the invention relates to an expandable tubular for sealing a hydrocarbon wellbore.
2. Description of the Related Art
Typically, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling to a predetermined depth, the drill string and bit are removed, and the wellbore is lined with a string of casing. Generally, it is desirable to provide a flow path for hydrocarbons from the surrounding formation into the newly formed wellbore. Therefore, after all casing has been set and cemented, perforations are formed in a wall of the liner string at a depth that equates to the anticipated depth of hydrocarbons. Alternatively, a lower portion of the wellbore may remain uncased, which is commonly referred to as an open-hole completion, so that the formation and fluids residing therein remain exposed to the wellbore.
A downhole packer is generally used to isolate a specific portion of a wellbore whether it is employed in a cased or uncased wellbore. There are many different types of packers; however, a recent trend in cased wellbore completion has been the advent of expandable tubular technology. It has been discovered that expandable packers can be expanded in situ so as to enlarge the inner diameter. This, in turn, enlarges the path through which both fluid and downhole tools may travel. Also, expansion technology enables a smaller tubular such as the expandable packer to be run into a larger tubular, and then expanded so that a portion of the smaller tubular is in contact with the larger tubular therearound. Expandable packers are expanded through the use of a cone-shaped mandrel or by an expansion tool with expandable, fluid actuated members disposed on a body and run into the wellbore on a tubular string. During the expansion operation, the walls of the expandable packer are expanded past their elastic limit. The use of expandable packers allows for the use of larger diameter production tubing, because the conventional slip mechanism and sealing mechanism are eliminated.
An expandable packer is typically run into the wellbore with a running assembly disposed at an end of a drill string. The running assembly includes an expansion tool, a swivel, and a running tool. Generally, the expansion tool is disposed at the bottom end of the drill string. Next, the swivel is disposed between the expansion tool and the running tool to allow the expansion tool to rotate while the running tool remains stationary. Finally, the running tool is located below the swivel, at the bottom end of the running assembly. The running tool is mechanically attached to the expandable packer through a mechanical holding device.
After the expandable packer is lowered to a predetermined point in the well, the expandable packer is ready to be expanded into contact with the wellbore or casing. Subsequently, the expansion tool is activated when a hydraulic isolation device, like a ball, is circulated down into a seat in the expansion tool. Thereafter, fluid is pumped from the surface of the wellbore down the drill string into the expansion tool. When the fluid pressure builds up to a predetermined level, the expansion tool is activated, thereby starting the expansion operation. During the expansion operation, the swivel allows the expansion tool to rotate while the packer and the running tool remain stationary. After the expandable packer has been expanded against the wellbore or casing, the running assembly is deactivated and removed from the well.
While expanding tubulars in a wellbore offer obvious advantages, there are problems associated with using the technology to create a packer through the expansion of one tubular into a wellbore or another tubular. For example, an expanded packer with no gripping structure on the outer surface has a reduced capacity to support the weight of the entire packer. This is due to a reduced coefficient of friction on the outer surface of the expandable packer. More importantly, the expansion of the expandable packer in an open-hole wellbore may result in an ineffective seal between the expanded packer and the surrounding wellbore.
An alternative to the expandable packer is an inflatable packer. Typically, the inflatable packer utilizes an expandable bladder to create a fluid seal within the surrounding wellbore or casing. In some instances, the bladder is expanded through actuation of a downhole pump. In other instances, the bladder is expanded through injection of hydraulic pressure into the tool. Inflation of the bladder forces a surrounding packing element to be inflated into a sealed engagement with the surrounding wellbore or string of casing.
The packer element in a typical inflatable packer is comprised of two separate portions. The first portion is an expandable rib assembly. Typically, the rib assembly defines a series of vertically overlaid reinforcing straps that are exposed to the surrounding casing. The straps are placed radially around the bladder in a tightly overlapping fashion. The second portion of the inflatable packer is an expandable sealing cover with a valve system. The sealing cover is a pliable material that surrounds a portion of the reinforcing straps. As the bladder and straps are expanded, the sealing cover expands and engages the surrounding pipe in order to effectuate a fluid seal. Thus, the rib assembly and the sealing cover portion of the packing element combine to effectuate a setting and sealing function.
While an inflatable packer offers an increased sealing capability over the expandable packer, there are potential problems associated with the inflatable packer. In one example, the inflatable packer rib assembly may be complex and costly to manufacture. In another example, the valve system is complex and may not function properly. More importantly, the inflatable packer reduces the hole size of the wellbore, thereby limiting the further drilling or exploration of the wellbore.
There is a need, therefore, for a packer that will create an effective seal by exerting pressure against a cased wellbore or an open-hole wellbore. There is a further need for a packer that will not reduce the diameter of the wellbore. There is yet a further need for a cost effective packer. Finally, there is a need for a liner assembly that will effectively isolate a zone within an open-hole or a cased wellbore.
The present invention generally relates to an apparatus and method for sealing a wellbore. In one aspect an apparatus for sealing a wellbore is provided. The apparatus includes a tubular body having an inner surface and an outer surface. The tubular body contains one or more apertures in a wall thereof to allow selective fluid communication between the inner surface and the outer surface. The apparatus further includes a swelling elastomer disposed around the outer surface of the tubular body. The swelling elastomer is isolated from wellbore fluid in an annulus. However, upon the application of an outwardly directed force to the inner surface of the tubular body, the tubular body expands radially outward causing the swelling elastomer to contact the wellbore while exposing the swelling elastomer to an activating agent via the one or more apertures, thereby causing the swelling elastomer to create a pressure energized seal with one or more adjacent surfaces in the wellbore.
In another aspect, a liner assembly for isolating a zone in a wellbore is provided. The liner assembly includes a deformable tubular and an upper and lower sealing apparatus disposed at either end of the deformable tubular. The upper and lower sealing apparatus comprises a tubular body, a swelling elastomer, and a deformable portion.
In yet another aspect, a method for sealing a wellbore is provided. The method includes running an expandable liner assembly on a drill string into the wellbore. The expandable liner assembly includes a deformable tubular and a sealing apparatus disposed at either end of the deformable tubular. The method further includes applying an outwardly directed force to the inner surface of a tubular body and causing the tubular body to expand radially outward. The method also includes exposing the swelling elastomer to an activating agent, thereby causing the swelling elastomer to expand outward deforming the deformable portion to create a pressure energized seal with one or more adjacent surfaces in the wellbore. The method includes expanding the deformable tubular.